Post-glacial range shift and plant community dynamics

Distributional changes facilitate adaptation and forge the evolutionary trends responsible for incipient speciation. Recently we have been researching the impact of a warming environment on the distribution and intraspecific diversification of a number of species. In the Australian Wet Tropics, Elaeocarpus species diverge across the Black Mountain Corridor (1, 2) long-lived rainforest conifer (Podocarpus elatus) shows climatic driven selective filtering (3, 4, 5, 6), and, turnover along altitudinal gradients from cool-temperate (Nothofagus spp.) to warm subtropical rainforest (Elaeocarpus spp.) in far-eastern Australia (7) reveal post-glacial trends.

Figure 1. Climate envelope models (altitudinal range shift) for Nothofagus moorei (blue) and Elaeocarpus grandis (yellow) in far-eastern Australia (Mt Warning Caldera) for 21 thousand years ago (fossil record support) during the Last Glacial Maximum (LGM) time period based on the Model for Interdisciplinary Research on Climate (MIROC 3.2.2) global climatic model, the current time period based on WorldClim data (1966-present) and an average of 13 global climatic models for 2050 (see 6 and 7). Darker shading indicates areas of higher elevation and lighter shading indicates areas of lower elevation.

Concerning community-turnover along altitudinal gradients of far-eastern Australia (7; Fig 1 and 2), the potential distributions of the two species closely associated with different rainforest types were modelled to infer the potential contribution of post-glacial warming on spatial distribution and altitudinal range shift (Fig 1). Climate envelope models were used to infer range shift differences between the two species in the past (21 thousand years ago), current and future (2050) scenarios, and to provide a framework to explain observed genetic diversity/structure (Fig 2 a-c). The models suggest continuing contraction of the highland cool temperate climatic envelope and expansion of the lowland warm subtropical envelope, with both showing a core average increase in elevation in response to post-glacial warming (Fig 2b).

Figure 2. a. Boxplots of area of overlap at each time for 10 paired replicate models. Area of overlap was measured as number of overlapping grid cells marked as core climate conditions for each species. b. Histograms of frequency of altitude values in the core climate condition grid cells for each species. Elaeocarpus grandis data is to the left and Nothofagus moorei to the right in each panel. Histograms of altitude in 100 m bands were based on the core climate suitability grid cells for each species pooled across the 10 replicates at each time. The dashed line on each plot indicates the mean altitude for each species. c. The entire (northern and southern) Nothofagus moorei occurrences (YETI and Atlas of NSW Wildlife), including genetic structure and diversity across whole range that comprises four major highland population groups. Darker shading indicates areas of higher elevation and lighter shading indicates areas of lower elevation.

We intend to apply this novel approach toward evolutionary theory to further study systems. Genomic (i.e. Next Generation Sequencing) approaches will provide additional tools to reliably predict future changes in genetic diversity and, as a consequence, adaptive potential of species to the rapid environmental changes anticipated this century.

Mellick R, Lowe A, Rossetto M (2011) Consequences of long- and short-term fragmentation on the genetic diversity and differentiation of a late successional rainforest conifer. Australian Journal of Botany 59, 351-362.